Genome (in)stability in bacteria

Bacteria can adapt
to environmental changes by adjusting gene expression, by controlling protein
activity, or by accumulation of beneficial mutations. The accumulation of
mutations can be detrimental for the bacteria. However, it is often the last
option to ensure survival in a specificenvironment. B. subtilis mutant strains lacking the key
enzymes involved in glutamate metabolism have a growth defect (Fig. A). For
instance, a strain lacking a functional glutamate dehydrogenase (GDH) rapidly
activates a second GDH that is inactive in common laboratory strains (Fig. B).
The suppressor mutants have always excised one part of a perfect direct repeat
that is present in the cryptic gdhCR gene and renders the
encoded GDH inactive (Fig. C). Moreover, theglutamate auxotrophy of a strain lacking
the glutamate synthase genes can be relieved by diverse mutations, illustrating
a flexible genome. We are currently working on the identification of novel factors that
affect the (in)stability of the B.
subtilis genome (Fig. D). Elucidating the underlying molecular mechanisms crucial
for genome maintenance and adaptability is important for understanding the
basic principles of molecular evolution. Moreover, the removal of factors
causing genome instability may help to engineer stable production strains for
industrial applications.

Figures. (A) Lack of GDH activity (here RocG)
affects physiology of the cell. (B) A functional GDH is important for growth of
B. subtilis on rich medium and the
bacteria rapidly acquire suppressor mutations. (C) A mutant strain lacking RocG
activates the second GDH GudB. (D) Transcription is important for mutagenesis
of the cryptic gudBCR gene.